With continuous development of network application, people have increasing requirements for a communication capacity, and a transmission rate of an optical communications network increases exponentially. Both a low-cost direct-detection optical communications system and a relatively-high-cost coherent-detection communications system that is based on a coherent receiver require implementation of larger-capacity transmission with lower costs.
In an existing direct-detection optical communications system, cost-effectiveness of the system is more emphasized, to implement a transmission capacity as large as possible with costs as low as possible. An optical signal in the direct-detection optical communications system has beat interference between different frequency components of the signal itself, also called signal-to-signal beat interference (SSBI), which compromises transmission performance of the direct-detection optical communications system.
To eliminate the SSBI and implement a larger transmission capacity, in a direct-detection optical communications system that is implemented using a digital signal processing (DSP) technology, a receiver sends a received optical signal to a DSP processing unit, and the DSP processing unit calculates SSBI in the optical signal by using a particular algorithm, and subtracts the SSBI from the optical signal according to a calculation result, so as to obtain an optical signal without the SSBI.
However, the foregoing method for receiving an optical signal and eliminating SSBI by using a DSP technology is not for a dual-polarization system and cannot implement receiving of a dual-polarization signal and elimination of SSBI from the dual-polarization signal.